Most interferometric electric field sensors use a two-beam interferometer such as a Mach Zehnder or Michelson interferometer which give low-contrast, broad and diffuse interference fringes which are difficult to measure with high precision. Another type of interferometer used in electric field sensors is the Fabry-Perot interferometer which is a resonant cavity bounded by two end mirrors separated so as to produce interference for certain allowed optical frequencies. However, the multiple beam Fabry-Perot type interference filters have conductive coatings on electro-optic bare crystals, and usually have antennas attached to the crystals in order to detect the electric field. These coatings and antennas distort the very electric field one is attempting to measure and result in biasing the measurements. Field sensors that have bare crystals utilize the property of the crystals which changes the polarization of the light that goes through them in the presence of electric field. But these sensors lack interferometric sensitivity. The interferometric sensors frequently are of the two-beam interference type with the attendant inability to give sharp, distinct fringes.